Wet etching solution

ABSTRACT

A wet etching solution includes hydrogen fluoride in an amount of about 0.1% to about 3% by weight of the etching solution, an inorganic acid in an amount of about 10% to about 40% by weight of the etching solution, the inorganic acid being one or more of nitric acid, sulfuric acid, and/or hydrochloric acid, a nonionic surfactant in an amount of about 0.0001% to about 5% by weight of the etching solution, the surfactant including one or ore of alkylphenol ethoxylate and/or ammonium lauryl sulfate, and water.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation application based on pending application Ser. No.11/892,076, filed Aug. 20, 2007, the entire contents of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate to a wet etching solution.More specifically, embodiments of the present invention relate to a wetetching solution having an improved oxide selectivity.

2. Description of the Related Art

In general, semiconductor devices and display devices, e.g., liquidcrystal displays (LCDs), organic light-emitting diode (OLED) displays,plasma display panels (PDPs), and so forth, may be fabricated by, e.g.,photolithography. Photolithography may include several processes, e.g.,etching.

Etching refers to a process of removing predetermined portions ofmaterial by wet etching, i.e., removal of material via application of achemical, or by dry etching, i.e., removal of material via plasma. Asopposed to dry etching, wet etching may be isotropic, i.e., removal ofmaterial in all directions at the same rate, thereby being suitable foruse in three-dimensional devices, e.g., metal wiring or contact holes ina semiconductor device. For example, portions of an oxide layer may beetched to form and/or to expose active regions, e.g., source/drainregions, gate regions, and so forth, on a semiconductor substrate.

Conventional wet etching may include a buffered oxide etchant (BOE),e.g., a diluted hydrofluoric acid (HF) solution containing ammoniumfluoride. However, conventional wet etchants may have low oxideselectivity, i.e., a ratio between etching rates of different materials,thereby causing incorrect etching of the oxide materials and ofstructures adjacent thereto, e.g., a metal silicide (MSi_(x)) gatestack. In other words, application of a conventional wet etchingsolution to an oxide material may cause excessive etching of elementsadjacent thereto, thereby damaging the adjacent elements. For example,the conventional BOE may have a very high etching ratio of metalsilicide to silicon oxide, e.g., remove portions of metal wiring aboutfive to ten times faster than portions of the oxide material.

SUMMARY OF THE INVENTION

Embodiments of the present invention are therefore directed to a wetetching solution, which substantially overcomes one or more of thedisadvantages of the related art.

It is therefore a feature of an embodiment of the present invention toprovide a wet etching solution exhibiting high oxide selectivity.

At least one of the above and other features and advantages of thepresent invention may be realized by providing a wet etching solution,including hydrogen fluoride in an amount of about 0.1% to about 3% byweight of the etching solution, an inorganic acid in an amount of about10% to about 40% by weight of the etching solution, the inorganic acidbeing one or more of nitric acid, sulfuric acid, and/or hydrochloricacid, a surfactant in an amount of about 0.0001% to about 5% by weightof the etching solution, the surfactant including one or ore ofalkylphenol ethoxylate and/or ammonium lauryl sulfate, and water. Thenonionic surfactant may be ammonium lauryl sulfate.

The wet etching solution may exhibit a selectivity ratio of siliconoxide to metal silicide of about 1:0.5 to about 1:3. The metal silicidemay include one or more of tungsten silicide, titanium silicide,molybdenum silicide, nickel silicide, tantalum silicide, and/or coppersilicide. The silicon oxide may be a boron phosphor silicate glass.

At least one of the above and other features and advantages of thepresent invention may be further realized by providing a wet etchingsolution, including an ammonium fluoride in an amount of about 0.1% toabout 10% by weight of the etching solution, an organic acid having atleast one carboxyl group in an amount of about 60% to about 98% byweight of the etching solution, and water. The organic acid may includeone or more of acetic acid, citric acid, glutaric acid, glycolic acid,formic acid, lactic acid, malic acid, maleic acid, oxalic acid, phthalicacid, succinic acid, tartaric acid, and/or propionic acid.

The wet etching solution may exhibit a selectivity ratio of siliconoxide to metal silicide in a range of about 1:0.5 to about 1:3. Themetal silicide may include one or more of tungsten silicide, titaniumsilicide, molybdenum silicide, nickel silicide, tantalum silicide,and/or copper silicide. The silicon oxide may be a boron phosphorsilicate glass.

At least one of the above and other features and advantages of thepresent invention may be also realized by providing a wet etchingsolution, including hydrogen fluoride in an amount of about 0.1% toabout 10% by weight of the etching solution, an ammonium fluoride in anamount of about 0.1% to about 10% by weight of the etching solution, anorganic acid having at least one carboxyl group in an amount of about30% to about 50% by weight of the etching solution, an alcohol in anamount of about 30% to about 50% by weight of the etching solution, andwater. The organic acid may include one or more of acetic acid, citricacid, glutaric acid, glycolic acid, formic acid, lactic acid, malicacid, maleic acid, oxalic acid, phthalic acid, succinic acid, tartaricacid, and/or propionic acid. The alcohol may include one or more ofmethanol, ethanol, butanol, and/or isopropyl alcohol.

The wet etching solution may exhibit a selectivity ratio of a siliconoxide to metal silicide in a range of about 1:1 to about 1:3. The metalsilicide may include one or more of tungsten silicide, titaniumsilicide, molybdenum silicide, nickel silicide, tantalum silicide,and/or copper silicide. The silicon oxide may be a boron phosphorsilicate glass.

DETAILED DESCRIPTION OF THE INVENTION

Korean Patent Application No. 10-2006-0078818, filed on Aug. 21, 2006 inthe Korean Intellectual Property Office, and entitled: “Silicon OxideSelective Wet Etching Solution,” is incorporated by reference herein inits entirety.

Hereinafter, exemplary embodiments of a wet etching solution accordingto the present invention will be described in more detail. The wetetching solution according to embodiments of the present invention mayprovide high oxide selectivity. In this respect, it is noted that“selectivity” refers to a ratio between different etch rates of anetching solution with respect to different materials, so that “highselectivity of oxides” refers to a high etching rate of oxides, ascompared to other materials, e.g., metal silicides. For example, anetching solution exhibiting high selectivity of oxides with respect tometal silicides may remove portions of oxides faster than portions ofmetal silicides.

Oxides may include silicon oxides, e.g., silicon dioxides,phosphorus-doped silicon glass (PSG), boron and phosphorus doped siliconglass (BPSG), boron-doped silicon glass (BSG), and so forth. Metalsilicides may include, e.g., tungsten silicide (WSi_(x)), titaniumsilicide (TiSi_(x)), molybdenum silicide (MoSi_(x)), nickel silicide(NiSi_(x)), tantalum silicide (TaSi_(x)), and copper silicide(CuSi_(x)), and so forth.

The wet etching solution according to an embodiment of the presentinvention may include about 0.1% to about 3% by weight of hydrogenfluoride (HF), about 10% to about 40% by weight of an inorganic acid,about 0.0001% to about 5% by weight of a surfactant, and water. Unlessindicated otherwise, all percentages refer hereinafter to weightpercentages based on a total weight of the wet etching solution.

Weight percentages of compounds described herein, e.g., hydrogenfluoride, inorganic acid, and surfactant, refer to pure, non-aqueousamounts of each of the components. For example, 2% by weight of hydrogenfluoride refers solely to an amount of pure hydrogen fluoride in the wetetching solution. In a case that hydrogen fluoride is used as an aqueoussolution, an amount of water in the aqueous hydrogen fluoride is not tobe included in the 2%. Further, weight percentages of water in the wetetching solution refer to water added as a remainder to balance thetotal weight percentage of the wet etching solution, plus any waterincluded in other components of the wet etching solution, e.g., aqueoushydrogen fluoride, aqueous inorganic acid, and/or aqueous nonionicsurfactant, in a case that such aqueous solutions are employed. Forexample, 80% by weight water may refer to 60% by weight of water addedto the wet etching solution and to 20% by weight of water included inaqueous components of the wet etching solution.

The hydrogen fluoride of the wet etching solution may increase oxideselectivity, thereby minimizing an etching rate of non-oxide components,e.g., metal silicides.

The inorganic acid of the wet etching solution may include one or moreof nitric acid (HNO₃), sulfuric acid (H₂SO₄), hydrochloric acid (HCl),and/or phosphoric acid (H₃PO₄), etc. For example, use of nitric acid mayincrease etching selectivity of silicon oxide relative to metalsilicide.

The surfactant of the wet etching solution may include, e.g.,alkylphenol ethoxylate, and/or ammonium lauryl sulfate (ALS), etc. Thesurfactant may be a nonionic surfactant may include both a hydrophilicgroup and a lipophilic group, thereby exhibiting miscibility in a largernumber of components, as compared to ionic surfactants. As such, thesurfactant may exhibit enhanced miscibility in the wet etching solutionof the present invention, as compared to conventional wet etchingsolutions.

In another embodiment of the present invention, the wet etching solutionmay include about 0.1% to about 10% by weight of an ammonium fluoride,about 60% to about 98% by weight of an organic acid having at least onecarboxyl group, and water.

The ammonium fluoride may increase oxide selectivity, thereby minimizingan etching rate of the metal silicide layer.

The organic acid may include one or more of acetic acid (C₂H₄O₂), citricacid (C₆H₈O₇), glutaric acid (C₅H₈O₄), glycolic acid (C₂H₄O₃), formicacid (CH₂O₂), lactic acid (C₃H₆O₃), malic acid (C₄H6O₅), maleic acid(C₄H₄O₄), oxalic acid (C₂H₂O₄), phthalic acid (C₈H₆O₄), succinic acid(C₄H₆O₄), tartaric acid (C₄H₆O₆), and/or propionic acid (C₃H₆O₂), etc.Use of the organic acid may minimize formation of particles on a surfaceof a semiconductor substrate upon application of the wet etchingsolution thereto.

In yet another embodiment of the present invention, the wet etchingsolution may include about 0.1% to about 10% by weight of hydrofluoricacid, about 0.1% to about 10% by weight of ammonium fluoride, about 30%to about 50% by weight of organic acid having at least one carboxylgroup, about 30% to about 50% by weight of alcohol, and the remainderwater.

Weight percentages of compounds described herein refer to pure,non-aqueous amounts of each of the components as described previouslywith respect to the first embodiment. Further, weight percentages ofwater in the wet etching solution refer to water added as a remainder tobalance the total weight percentage of the wet etching solution, plusany water included in other components of the wet etching solution.

The organic acid may include one or more of acetic acid (C₂H₄O₂), citricacid (C₆H₈O₇), glutaric acid (C₅H₈O₄), glycolic acid (C₂H₄O₃), formicacid (CH₂O₂), lactic acid (C₃H₆O₃), malic acid (C₄H6O₅), maleic acid(C₄H₄O₄), oxalic acid (C₂H₂O₄), phthalic acid (C₈H₆O₄), succinic acid(C₄H₆O₄), tartaric acid (C₄H₆O₆), and/or propionic acid (C₃H₆O₂), etc.

The alcohol may include one or more of methanol, ethanol, butanol,and/or isopropyl alcohol, etc. The use of alcohol may minimize wettingof the surface of a semiconductor substrate, thereby decreasing theetching rate of the substrate and reducing formation of particlesthereon.

EXAMPLES

Nine (9) wet etching solutions were prepared according to embodiments ofthe present invention, i.e., Examples 1-9. Additionally, ten (10)comparative wet etching solutions were prepared, i.e., ComparativeExamples 1-10. Examples 1-3 were prepared according to the firstembodiment, Examples 4-7 were prepared according to the secondembodiment, and Examples 8-9 were prepared according to the thirdembodiment.

Each wet etching solution was evaluated in terms of its etching rate. Inparticular, each wet etching solution was used to etch a boron phosphorsilicate glass (BPSG) layer having an initial thickness of 9,000angstroms and a titanium silicide (TiSi_(x)) layer having an initialthickness of 1,000 angstroms. The layers used were blanket layers.

Each layer was dipped separately in the wet etching solution for 4 min.Next, a thickness of each layer was measured to determine a thicknessdifference with respect to a respective initial thickness. The thicknessdifference was converted to an etch rate expressed in angstroms/min. Theresults are reported in Tables 1-3, which refer to wet etching solutionsprepared according to the first, second, and third embodiments,respectively.

Example 1

a wet etching solution was prepared to include 0.2 wt % of HF, 25 wt %of HNO₃, 0.1 wt % of ALS (Fluka), and the remainder water, and wasevaluated in terms of etch rate.

Example 2

a wet etching solution was prepared to include 1 wt % of HF, 10 wt % ofHNO₃, 1 wt % of ALS, and the remainder water, and was evaluated in termsof etch rate.

Example 3

a wet etching solution was prepared and evaluated according to theprocess described in Example 2, with the exception of using 5 wt % ofALS.

Comparative Example 1

a wet etching solution was prepared to include a conventional HFsolution containing ammonium fluoride and a surfactant, i.e. bufferedoxide etchant (BOE). The wet etching solution was evaluated in terms ofetch rate.

Comparative Example 2

a wet etching solution was prepared and evaluated according to theprocess described in Example 2, with the exception of using no HNO₃.

Comparative Example 3

a wet etching solution was prepared and evaluated according to theprocess described in Example 2, with the exception of using ethyleneglycol (EG) as a solvent instead of water. The wet etching solutioncontained EG in an amount of at least 80 wt % based on the total weightof the etching solution.

Comparative Example 4

a wet etching solution was prepared and evaluated according to theprocess described in Example 2, with the exception of using SynperonicPE/L64® (Uniqema, Inc., UK) as a surfactant, instead of ALS.

The results of Examples 1-3 and Comparative Examples 1-4 are reported inTable 1 below.

TABLE 1 Wet Etching Solutions According to the First Embodiment Etchingrate of Etching rate of BPSG layer Etching ratio Ex. No. TiSi_(x) layer(Å/min) (Å/min) (TiSi_(x):BPSG) Example 1 200 100   2:1 Example 2 700300 2.33:1 Example 3 700 250  2.8:1 Comp. Example 1 2,000 200   10:1Comp. Example 2 1,000 55 18.18:1  Comp. Example 3 600 150   4:1 Comp.Example 4 680 150 4.53:1

Referring to Table 1, wet etching solutions of Comparative Examples 1-4exhibited a selectivity ratio of the TiSi_(x) layer to the BPSG layer ofabout 10:1, 18.18:1, 4:1, and 4.53:1, respectively. On the other hand,all the wet etching solutions prepared according to an embodiment of thepresent invention, i.e., Examples 1-3, exhibited an etching rate of theTiSi_(x) layer to the BPSG layer as a ratio of about 2:1, 2.33:1, and2.8:1, respectively. These results indicate that the wet etchingsolutions according to the present invention have a higher etchingselectivity for the silicon oxide layer, as compared to those of the wetetching solutions of Comparative Examples 1-4.

Example 4

a wet etching solution was prepared to include 2 wt % of ammoniumfluoride, 90 wt % of acetic acid, and 8 wt % of water, and was evaluatedin terms of etch rate.

Example 5

a wet etching solution was prepared to include 1 wt % of ammoniumfluoride, 98 wt % by weight of acetic acid, and 1 wt % of water, and wasevaluated in terms of etch rate.

Example 6

a wet etching solution was prepared and evaluated according to theprocess described in Example 5, with the exception of using formic acidinstead of acetic acid.

Example 7

a wet etching solution was prepared and evaluated according to theprocess described in Example 5, with the exception of using propionicacid instead of acetic acid.

Comparative Example 5

a wet etching solution was prepared and evaluated according to theprocess described in Comparative Example 1.

Comparative Example 6

a wet etching solution was prepared and evaluated according to theprocess described in Example 4, with the exception of using no aceticacid.

Comparative Example 7

a wet etching solution was prepared and evaluated according to theprocess described in Example 4, with the exception of using hydrochloricacid (HCl) instead of the acetic acid.

The results of Examples 4-7 and Comparative Examples 5-7 are shown inTable 2 below.

TABLE 2 Wet Etching Solutions According to the Second Embodiment Etchingrate of Etching rate of BPSG layer Etching ratio Ex. No. TiSi_(x) layer(Å/min) (Å/min) (TiSi_(x):BPSG) Example 4 620 280 2.21:1 Example 5 200258 0.76:1 Example 6 983 421 2.33:1 Example 7 1,203 530 2.27:1 Comp.Example 5 2,000 200   10:1 Comp. Example 6 1,000 55 18.18:1  Comp.Example 7 2,800 480 5.83:1

Referring to Table 2, the wet etching solutions of Comparative Examples4-7, exhibited an etching rate of the TiSi_(x) layer to the BPSG layerof about 10:1, 18.18:1, and 5.83:1, respectively. On the other hand, wetetching solutions prepared according to the present invention, i.e.,Examples 4-6, exhibited an etching rate of the TiSi_(x) layer to theBPSG layer of about 2.21:1, 0.76:1, 2.33:1, and 2.27:1, respectively.These results indicate that wet etching solutions according to thepresent invention have a higher etching selectivity for the siliconoxide layer, as compared to those of the wet etching solutions ofComparative Examples 5-7.

Example 8

a wet etching solution was prepared to include 0.3 wt % of hydrofluoricacid, 2 wt % of ammonium fluoride, 48 wt % of acetic acid, 48 wt % ofisopropyl alcohol, and the remainder water, and was evaluated in termsof etch rate.

Example 9

a wet etching solution was prepared and evaluated according to theprocess of Example 8, with the exception of using methanol instead ofisopropyl alcohol.

Comparative Example 8

a wet etching solution was prepared and evaluated according to theprocess of Comparative Example 1.

Comparative Example 9

a wet etching solution was prepared and evaluated according to theprocess of Example 8, with the exception of using no acetic acid, i.e.,water was added in an amount corresponding to the acetic acid.

Comparative Example 10

a wet etching solution was prepared and evaluated according to theprocess of Example 8, with the exception of using hydrochloric acidinstead of acetic acid.

Results of Examples 8-9 and Comparative Examples 8-10 are shown in Table3 below.

TABLE 3 Wet Etching Solutions According to the Third Embodiment Etchingrate of Etching rate of BPSG layer Etching ratio Ex. No. TiSi_(x) layer(Å/min) (Å/min) (TiSi_(x):BPSG) Example 8 510 300  1.7:1 Example 9 800210 3.81:1 Comp. Example 8 2,000 200   10:1 Comp. Example 9 1,000 5518.18:1  Comp Example 10 2,800 480 5.83:1

Referring to Table 3, the wet etching solutions of Comparative Examples8-10 exhibited an etching ratio of the TiSi_(x) layer to the BPSG layerof about 10:1, 18.18:1, and 5.83:1, respectively. On the other hand, wetetching solutions prepared according to an embodiment of the presentinvention, i.e., Examples 8-9, exhibited an etching ratio of theTiSi_(x) layer to the BPSG layer of about 1.7:1 and 3.81:1,respectively. These results indicate that wet etching solutionsaccording to the present invention may have high etching selectivity forthe silicon oxide layer, as compared to those of the wet etchingsolutions of Comparative Examples 8-10.

The wet etching solutions according to embodiments of the presentinvention may be advantageous in providing a higher selectivity foroxides relative to, e.g., metal silicide, as compared to conventionalwet etching solutions. Accordingly, wet etching solutions according toembodiments of the present invention may facilitate faster and moreefficient removal of silicon oxide portions, e.g., at least two times(2×) faster, without causing substantial damage to adjacent non-oxideelements, e.g., titanium silicide elements, as compared to, e.g.,Comparative Examples 1-10. Further, the wet etching solutions accordingto embodiments of the present invention may exhibit superior etchselectivity for BPSG.

Exemplary embodiments of the present invention have been disclosedherein, and although specific terms are employed, they are used and areto be interpreted in a generic and descriptive sense only and not forpurpose of limitation. Accordingly, it will be understood by those ofordinary skill in the art that various changes in form and details maybe made without departing from the spirit and scope of the presentinvention as set forth in the following claims.

1. A wet etching solution, comprising: hydrogen fluoride in an amount ofabout 0.1% to about 3% based on a total weight of the wet etchingsolution; an inorganic acid in an amount of about 10% to about 40% basedon the total weight of the wet etching solution, the inorganic acidbeing one or more of nitric acid, sulfuric acid, and/or hydrochloricacid; a surfactant in an amount of about 0.0001% to about 5% based onthe total weight of the wet etching solution, the surfactant includingone or more of alkylphenol ethoxylate and/or ammonium lauryl sulfate;and water, wherein the wet etching solution exhibits a selectivity ratioof silicon oxide to metal silicide of about 1:0.5 to about 1:3.
 2. Thewet etching solution as claimed in claim 1, wherein the nonionicsurfactant is ammonium lauryl sulfate.
 3. (canceled)
 4. The wet etchingsolution as claimed in claim 1, wherein the selectivity ratio forsilicon oxide to each of tungsten silicide, titanium silicide,molybdenum silicide, nickel silicide, tantalum silicide, and coppersilicide, is about 1:0.5 to about 1:3.
 5. The wet etching solution asclaimed in claim 1, wherein the selectivity ratio of boron phosphorsilicate glass to metal silicide is about 1:0.5 to about 1:3. 6.-16.(canceled)
 17. A method for selectively etching a silicon oxide layerusing the wet etching solution according to claim
 1. 18.-19. (canceled)20. The wet etching solution as claimed in claim 1, wherein thesurfactant is alkylphenol ethoxylate and excludes ammonium laurylsulfate.
 21. The wet etching solution as claimed in claim 20, whereinthe amount of the surfactant is about 0.0001% to less than 1% based onthe total weight of the wet etching solution.